Conventional containers for fluids may have rigid walls or flexible walls. Containers with rigid walls have a defined permanent volume for containing fluids and containers with flexible walls have variable or changeable volumes. Conventional containers include, but are not limited to, bottles, canisters and bags. Such containers may be used for a variety of purposes, including obtaining and holding fluid samples and containing standard gas mixtures that may be used for calibration of analytical instruments. As used herein, the term “fluid” includes gases and/or liquids. There are many configurations of such containers that have been developed and specialized for particular uses.
Gas mixtures under pressure are effective for preparing standard fluid mixtures in industrial quantities and preferably with comparably high concentration of one (or more) components in a carrier fluid. Gas mixtures under high pressure are typically stored in containers with rigid walls. For laboratory use, such gas mixtures may be diluted with additional carrier fluid to a desired concentration of a specific component in order to prepare a standard mixture. Conventional containers for transporting, preserving and use of such standard mixtures may be containers having flexible walls comprised of an inert, low-permeability material. Materials having low sorption on the walls for the components contained are preferred to increase the integrity of the mixture. Containers with flexible walls, also referred to as sampling bags, are widely used for fluid sampling, air sampling and liquid sampling. Materials such as Kynar and Tedlar are widely used for making such containers.
In order to obtain a representative sample or prepare an accurate standard, the containers must be properly prepared prior to filling. Typically, the bags are flushed with neutral gas and subjected to high vacuum to substantially remove all the fluid from the container with strong vacuum pumps. The bags should be purged and flushed to cause desorption of any residue and their volume should reduced to substantially zero. Any adsorbed residue or residual gas may contaminate any prepared fluid mixture or sample of fluid put in a poorly prepared bag.
Containers with rigid walls and flexible walls both have their own advantages and disadvantages. The disadvantages of containers with rigid walls include their extremely high price and expensive maintenance; they are bulky and, thus, their storage, transportation, and mailing costs are expensive; they have to be over pressurized when delivery of gas vapors or mixtures is needed; and completely vacuumed before used for fluid sampling.
Another drawback of sampling with containers with rigid walls is that after removing a portion of the sample from the container, the pressure in the canister may be reduced below atmospheric pressure and additional carrier gas (noble gas for example) may be added to increase the pressure back to atmospheric pressure. This process dilutes the sample or standard and analysis requires compensation for the additional carrier gas.
One method of filling container with rigid walls is to create a vacuum within the container. The driving force to get fluid into the container is provided by this vacuum. A small sampling pump cannot create a sufficient vacuum within the container; therefore, strong specialized vacuum pumps are needed.
An alternative to the containers with rigid walls are containers with flexible walls or bags. For containers with flexible walls, two methods of filling are known and widely used: (OSHA Technical Manual—Directive Number: 08-05 (TED 01), Effective Jun. 24, 2008)
The first method comprises delivering the fluid or fluid sample, e.g. industrial ambient air, into the bag with an external pump. A schematic of this method is depicted in FIG. 8. The sampling method includes a bag 40, a pump 50 powered by a battery 52, and tubing 44 connecting pump 50 to bag 40. Typical personal sampling pumps are suitable for this sampling method.
Bags may be used for preparing standard fluid mixtures or for sampling. When preparing standard fluid mixtures, first the bag is filled with an appropriate measured volume of carrier fluid. The clean carrier gas is dosed with a quantity of fluid, typically, added by pump or syringe as shown in FIG. 8. When used for sampling, a sample of an environment is delivered through the pump and tubing into the bag. The bag is then sealed and sent to a laboratory for analysis.
There are advantages and disadvantages to using this method with sampling bags. The disadvantages include the cost, inaccuracy, and potential contamination from using an external pump to deliver and withdraw the fluid mix. The contamination or inaccuracy can occur from sorption and desorption of some chemicals or components of gas mixture or sample on the walls of the tubes, internal part of the pumps, filters, tubing and connectors. The same problem is caused by sorption of chemical components on the walls of the sampling bag. Even with cleaned walls, active adsorbing sites on the walls can reduce the concentration of certain chemicals when the sample gas is subsequently removed and analyzed. This adsorption may decrease the recovery of certain chemical compounds up to 15%. The recovery rates of this method can be improved with the use of expensive stationary pumps and connection tubes, especially for sampling of trace components.
These methods may also be improved by using a different configuration of pump and the sampling bag. In this configuration shown in FIG. 9, the flexible sampling bag 40 is hermetically sealed within an outer container 60 with rigid walls. The air from the outer container is evacuated through tubing 44 by a pump 50. The pump may be powered by battery 52. As the pressure in the outer container 60 is reduced and bag 40 expands and air from the surrounding environment enters the bag 40. Thus the vacuum outside of the bag 40 and within the container 60 is a driving force for fluid sampling. In the embodiment shown in FIG. 9, the inlet of a sampling bag is connected directly with the ambient fluid. This method does not suffer from one of the major drawbacks of the configuration shown in FIG. 8. The sample taken in the configuration of FIG. 9 does not contact the pump 50 or tubing 44, therefore, there is no sorption or cross-contamination from the walls of the tubing 44, connectors, filter or parts of the sampling pump 50. The other drawbacks of the configuration of FIG. 8 are, however, still persisting in the alternative configuration of FIG. 9, for example, the components is bulky and heavy; the equipment is expensive; the pump requires a battery and frequent maintenance; the sorption on the walls of the bag is the same as described above.
Various embodiments of these methods are described United States patents. For example, U.S. Pat. No. 3,866,474 to Hasselman describes a system in which a sample and an inert gas are drawn into a sample bag within a hermetically sealed container. U.S. Pat. No. 3,965,946 to D'Alo describes improvements in the construction of the outer container. U.S. Pat. No. 5,437,201 to Krueger describes a method of repeatedly purging the sampling bag within the outer container. More sophisticated devices are disclosed in U.S. Pat. No. 5,714,696 to Yemans. The devices attempt to overcome the disadvantages of the system to obtain samples with very low contamination levels. U.S. Pat. No. 6,338,282 to Gilbert describes an apparatus for collection of liquids proves the versatility of this approach. More recently U.S. Pat. No. 6,993,985 to Srebro describes using the apparatus combined in single device yet connected to external vacuum source. Despite of cleanliness suggested by this method, it is using comparably heavy, bulky and expensive equipment requiring calibration and battery maintenance.
An attempt to avoid using pumps in the sampling process is disclosed in U.S. Pat. No. 4,546,659 to Gill et al. This patent discloses a small (10 ml) envelope for the collection of atmospheric air samples for subsequent analysis. The envelope is formed of first and second opposed panels of flexible, gas impermeable material which are peripherally sealed to define a collection chamber. The envelope contains expandable means such as a spiral spring or foam. The expandable means transfer force to the walls via guard plate and large septum. These envelopes have several disadvantages. For example, the expandable means in contact with the sampled fluid increases the potential for adsorption by the inner elements, i.e. the spring or, especially, any foam. Further, the expandable means prevents full evacuation of the contents of the envelope. This large surface area for absorption allows only high concentrations of chemical compounds to be sampled with acceptable recovery and accuracy. Further, the envelope cannot be reused, because the sampling volume would need to be purged several times to clean the envelope, however, the self sealing septum of the envelope does not allow such a procedure.
There is a need for a sampling bag that is capable of fluid delivery or fluid sampling without an external source of energy such as pressure or vacuum pumps, without outer containers with rigid walls, without tubes, and tube connectors. Further there is a need for a sampling bag that creates it own driving force for sample collection. There is also a need for a sampling bag that reduces external contamination of a standard mixture or a sample.
There is a further need for a container for a standard mixture that does not require addition of further carrier gases and any associated concentration calculations and volume compensation related to the use of container with rigid walls.
There is further need for sampling bag that allows use of substantially all of the sampled volume. There is a further need for such a device that is inexpensive, easy to manufacture, designed for multiple uses, may be used with both sampling bags specially designed and conventional sampling bags, light, not bulky, capable of use by hand or may be self operated and easy to transport, and/or intrinsically safe in use.